A prior art wire device includes a piece of wire wound one and a half times on one plane in a rectangle to form two legs which define the longitudinal sides thereof. Such a paper clip is defective, however, as a device for firmly clamping things of a certain thickness without displacement. More particularly, when bulky sheets of paper are inserted between the legs, the tips of these legs come off of the surface of the paper, thereby leaving the clamping force concentrated on the edge of the paper. The loose legs easily catch other articles and the clip itself may slip off the paper bundle and the turned-up legs present difficulties when the clipped sheets of paper have to be stacked in pile. Further, the stress concentrates on the narrow part at the root of the legs, exceeding the elastic limit of the wire. The paper clip of this type clamps sheets of paper with its long legs substantially normal to the edge of the sheets but not parallel thereto. When one skims through the content of the paper sheets clamped with the clip by turning the pages, the tips of the leg get in the way and make it difficult to fully open the page. If, on the other hand, the page is forced open, the clip may slip off. Thus, the paper clip of this type is fundamentally defective as a device for clamping thick bundle of sheets.
A so-called double-clip which is a clamping metal made of hard steel plate having a predetermined width, formed as an isosceles triangle in cross section and provided with a lever for opening the mouth of the clip.
Said double clip is limited in the package thickness it can accommodate by the height of the back member which is the base of the isosceles triangle, and therefore it can only be used to clamp articles thinner than the height of the height dimension of the back member. In most cases, the back of the clamping metal protrudes perpendicularly from the surface of the article at the edge thereof. This protrusion causes various inconveniences when the articles are stacked.
Further, when one goes through the papers by turning the pages, said lever may get in the way. Because of its construction, said double clip is more costly to manufacture and is thus considerably more expensive than other clamping devices.
In view of the defects found in the conventional clamping devices, the present invention aims to provide a novel clamping device which fulfills the requirements such that: it can firmly clamp thick articles such as sheets of paper; the clamping member may snugly attach to the both surfaces of the article at its edge; it can clamp an article with its clamping arms extending close to the edge so that the pages can be fully turned open to the extreme edge; the clamping means will not twist or damage the paper in use; the construction is simple enough to be manufactured at low cost.